Abstract: We
report
our
investigations into the fabrication of
nanostructures of
poly(p-phenylene vinylene) via direct scanning near-field
lithography of its soluble precursor. Our technique is based on the
spatially selective inhibition of the precursor solubility by exposure
to the ultraviolet optical field
present at the apex of commercially available, Au-coated near-field
probes with aperture diameters between 40 and 80nm (75 nm).
After development in methanol and thermal conversion under vacuum we
obtain features with a minimum dimension of
160 nm. We analyse our results via tapping mode atomic force
microscopy, and find a clear phase contrast between the
core and the centre of the lithographed features, corroborating the
hypothesis that hard, fully insolubilised
regions are surrounded by a gel-like phase, which we estimate of the
order of 110Ð130nm for the smallest features, by
comparing our experiments with simulations carried out using a
Bethe-Bouwkamp model. Use of such model also
allows
us to discuss the influence of probe size, tipÐsample distance, and
film thickness on the resolution of the
lithographic process. We demonstrate the use of the technique for the
direct writing of two-dimensional periodic structures
with intentional defects and a periodicity relevant to applications in
the visible range.
Abstract: The
efficiency of
light-emitting diodes based on
poly[(2-methoxy)-5-(2[prime]-ethyl-hexyloxy)-1,4-phenylenevinylene]
increases upon formation of interlayers, on top of
poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid
(PEDOT:PSS), made of acid-initiated cross-linkable polyfluorenes. The
use of this type of polymers allows for the formation of thicker
interlayers leading to higher efficiencies when comparing with similar
devices with interlayers formed by the parent non-cross-linkable
polymers. This efficiency increase is attributed to a combination of
electron and exciton confinement away from PEDOT:PSS.
Use
of cross-linkable polyfluorene in the fabrication of multilayer
polyfluorene-based light-emitting diodes with improved efficiency
A.
Charas, H. Alves, L. Alcacer and
J. Morgado
Appl.
Phys. Lett. 89, 143519 (2006);
DOI:10.1063/1.2360243
Abstract: The
authors report the use of a cross-linkable polyfluorene to fabricate
multilayer light-emitting diodes (LEDs), thereby avoiding the
restriction to combine polymeric solutions in different solvents. In
particular, we find that for LEDs fabricated with a hole-injection
layer of poly(3,4-ethylenedioxythiophene) doped with polystyrene
sulfonic acid (PEDOT), with magnesium cathodes and with
poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), as emissive
layer, its electroluminescence efficiency increases from 2
to 5.5 cd/A upon insertion of the cross-linked polyfluorene
between PEDOT and F8BT. This efficiency increase is attributed to an
improvement of charge carrier balance within the F8BT emissive layer
and a reduction of exciton quenching at PEDOT interface.
Luminescence
properties of composites made of a europium(III) complex and
electroluminescent polymers with different energy gaps
Jorge Morgado,
Ana Charas,
Jose A
Fernandes, Isabel S Goncalves, Luis D. Carlos and Luis Alcacer
J.
Phys. D: Appl. Phys. 39 (2006)
3582-3587
DOI:10.1088/0022-3727/39/16/009
Abstract. We present
the optoelectronic properties of composites made of a europium(III)
complex, Eu(NTA)3 phen (where
NTA=1-(2-naphthoyl)-3,3,3-trifluoroacetonate; phen=1,10-phenantroline),
dispersed in three electroluminescent polymers, namely,
poly(N-vinylcarbazole), poly(9,9-dioctylfluorene) and
poly(9,9-dioctylfluorene-alt-benzothiadiazole). We find that the photo-
and electroluminescence (EL) properties of these composites are well
rationalized in terms of the relative position of the frontier levels
of the host polymers and of the europium complex. We find also that
charge recombination at the europium complex sites plays a key role on
the EL properties of the composites.
Self-assembly
surface modified indium-tin oxide anodes for single-layer
light-emitting diodes
Jorge
Morgado, Nunzio
Barbagallo, Ana Charas, Manuel Matos, Luis Alcacer and Franco Cacialli
J. Phys. D:
Appl. Phys. 36 (2003) 434-438
doi:10.1088/0022-3727/36/5/304
Abstract.
We study the effect of indiumÐtin oxide surface modification by
self
assembling of highly polar molecules on the performance of single-layer
light-emitting diodes (LEDs) fabricated with polyfluorene blends and
aluminium cathodes. We find that the efficiency and light-output of
such LEDs is comparable to, and sometimes better than, the values
obtained for LEDs incorporating a hole injection layer of
poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic
acid. This effect is attributed to the dipole-induced work function
modification of indiumÐtin oxide.
D. Graf, J. S.
Brooks, E. S.
Choi, M. Almeida, R. T. Henriques, J. C. Dias and S. Uji
PHYSICAL REVIEW
B 75, 245101 2007
DOI:
10.1103/PhysRevB.75.245101
Abstract:
The
quantum interference QI of charge carriers in a
magnetic field is obtained in the organic conductor (Per)2Au(mnt)2 by suppressing the
charge-density-wave CDW state with pressure. The QI
oscillation amplitude
exhibits a temperature-dependent scattering rate, indicative of an
inhomogeneous metal-CDW ground
state. The QI oscillation frequency reveals a Fermi-surface topology in
close agreement with band-structure
predictions. The value of the frequency is quite small, making the
limit of constructive interference experimentally
accessible.